US 7019693 B2 Abstract The altitude of a communications device, which communicates with a communications system via at least one antenna, is estimated. The altitude estimation is based at least on altitude information of said at least one antenna. The altitude estimate of the communications device may be based on a two-dimensional location estimate for the communications device and on information representing three-dimensional location of said at least one antenna of said communication system. The two-dimensional location estimate and the altitude estimate may be sent to the communications device as location assistance information.
Claims(37) 1. A method for estimating altitude of a communications device, comprising the step of:
estimating a two-dimensional location estimate of the communications device based on signal measurements relating to at least two antennas of a communications system; and
estimating the altitude of the communications device based at least on altitudes of said at least two antennas of a communications system and on the two-dimensional location estimate of the communications device.
2. A method as defined in
3. A method as defined in
4. A method for estimating altitude of a communications device, comprising the step of:
estimating a two-dimensional location estimate of the communications device based on signal measurements relating to at least two antennas of a communications system and based on identity information of at least two cells corresponding to said at least two antennas of said communications system; and
estimating the altitude of the communications device based at least on altitudes of said at least two antennas of said communications system and on the two-dimensional location estimate of the communications device.
5. A method as defined in
6. A method as defined in
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14. A method as defined in
15. A method as defined in
16. A method as defined in
17. A method as defined in
18. A method for providing location assistance information to a communications device communicating with a communications system via at least two antennas of said communications system, said method comprising:
estimating a two-dimensional location estimate of the communications device based on signal measurements relating to said at least two antennas of said communications system;
estimating an altitude estimate of the communications device based at least on altitude information of said at least two antennas; and
determining location assistance information based on the two-dimensional location estimate and the altitude estimate of the communications device.
19. A method as defined in
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22. A method as defined in
23. A communications system, said communications system comprising:
first estimation means for estimating a two-dimensional location estimate of a communications device based on signal measurements relating to at least two antennas of said communications system;
storage means for storing antenna information representing at least altitudes of said at least two antennas of said communications system; and
second estimation means for estimating an altitude of said communications device based at least on said altitudes of said at least two antennas of said communications system and on the two-dimensional location estimate of the communications device.
24. A communications system as defined in
determination means for determining location assistance information based on said two-dimensional location estimate and said altitude estimate of the communications device.
25. A communications system as defined in
wherein said antenna information represents three-dimensional locations of antennas of said communications system.
26. A communications system as defined in
determination means for determining location assistance information based on said two-dimensional location estimate and said altitude estimate of the communications device.
27. A communications system as defined in
third estimation means for estimating accuracy of said altitude estimate for a communications device.
28. A communications system as defined in
29. A network element for a communications system, said network element comprising:
first estimation means for estimating a two-dimensional location estimate of a communications device based on signal measurements relating to at least two antennas of said communications system;
first determination means for determining antenna information representing at least altitudes of said at least two antennas of said communications system; and
second estimation means for estimating an altitude of the communications device based at least on said altitudes of said at least two antennas of said communications system and on said two-dimensional location estimate of the communications device.
30. A network element as defined in
third determination means for determining location assistance information based on said two-dimensional location estimate and said altitude estimate of the communications device.
31. A network element as defined in
wherein said antenna information represents three-dimensional locations of antennas of said communications system.
32. A network element as defined in
third determination means for determining location assistance information based on said two-dimensional location estimate and said altitude estimate of the communications device.
33. A network element as defined in
third estimation means for estimating accuracy of said altitude estimate for a communications device.
34. A network element as defined in
35. A network element as defined in
36. A computer readable medium containing executable computer program instructions which, when executed by a data processing system, cause said data processing system to perform a method comprising
estimating a two-dimensional location estimate of the communications device based on signal measurements relating to at least two antennas of a communications system; and
estimating an altitude of the communications device based at least on altitudes of said at least two antennas of a communications system and on the two-dimensional location estimate of the communications device.
37. A method for providing location assistance information to a communications device communicating with a communications system, said method comprising:
estimating a two-dimensional location estimate of the communications device based on signal measurements relating to at least two antennas of a communications system;
estimating an altitude estimate of the communications device based at least on altitude information of said at least two antennas of the communications system and on the two-dimensional location estimate; and
determining location assistance information based on the two-dimensional location estimate and the altitude estimate of the communications device.
Description 1. Field of the Invention The invention relates in general to estimating three-dimensional location of a communications device. 2. Description of the Related Art Positioning services have become very popular in the recent years. Positioning refers here to determining the location of a communications device. The communications device may be capable of determining its position based on signals it receives. The signals can be sent either from a specific positioning system or, for example, from a cellular communications system. Alternatively, the communications device may act as a measurement device and send measurement results to a further unit, which then determines the location of the communications device. Positioning services may be used simply for locating the communications device. The location of the communications device may, for example, be shown on a map at the display of the communications device. Alternatively, it is possible to provide location-dependent services, for example, for users of a communication system. The location of the communications device may affect the content of a location-dependent service. A further option is that the location of the communications device is used for determining whether the service is provided to the communications device at all. The most widely used positioning system is the Global Positioning System (GPS). GPS positioning is based on measuring relative time of arrival of signals sent simultaneously from a number of GPS satellites. The location of a GPS receiver is determined by determining the distance between GPS satellites and the GPS receiver using time of arrival measurement results together with the exact GPS time. The locations of the GPS satellites can be determined based on navigation information carried in the GPS signals. The navigation information includes both data unique to the transmitting satellite and data common to all satellites. The navigation information contains time information, satellite clock correction data, ephemeris (precise orbital parameters), almanac (coarse orbital parameters), health data for all satellites, coefficients for the ionospheric delay model and coefficients to calculate the Universal Coordinated Time (UTC) from the GPS system time. In theory, three time of arrival measurements would be enough to calculate the GPS receiver's position and also the velocity, if the exact GPS time is known to the GPS receiver. In practice, a GPS receiver has low-cost, low-accuracy local oscillator as a local clock. Therefore a fourth time of arrival measurement is needed to determine the difference between the local time and the GPS time. GPS positioning is dependent on obtaining accurate GPS time and navigation information and on performing the distance measurements. For carrying out GPS positioning successfully, signals from three or four GPS satellites need to be received properly for demodulating navigation data needed for the distance measurements. For shortening the time-to-first-fix, it is possible to provide information about the rough location of the GPS receiver to the GPS receiver. Assisted GPS (A-GPS) refers to sending some assistance information to a GPS receiver for helping the receiver to locate itself based on the GPS signals. One example of the assistance information for GPS is information on the rough location of the GPS receiver. By providing a rough estimate of the location of the GPS receiver as location assistance information, the response time of GPS positioning can be shortened. A communications system, for example a cellular telecommunications system, may be used for transmitting the location assistance information to a communications device incorporating, in addition to the functionality needed for communicating with the communications system, a GPS receiver for receiving GPS signals. The communications system may optionally be equipped with a plurality of reference GPS receivers for obtaining other assistance information than only the rough estimate of the GPS receiver. In connection with location a mobile station (a communications device) of a cellular telecommunication system, mobile-based positioning refers to determining the location in the mobile station based on the signals received from the cellular telecommunications network or from an external system, such as from the GPS. Mobile-assisted positioning refers to the cellular telecommunication network determining the location of the mobile station, but using information sent by the mobile station. MS-based A-GPS, for example, thus refers here to a location method, where location assistance information is sent to a communications device and the communications device determines its location using the location assistance information and the measurements it has performed on received GPS signals. On the other hand, MS-assisted A-GPS refers here to a location method, where location assistance information is sent to a communications device, which then performs the measurements on the received GPS signals and sends the measurements back to the telecommunication network, which finally uses such measurements for determining the device location. Both in MS-based and in MS-assisted A-GPS, the communication device uses location assistance information to shorten the time needed to perform the measurements on the received GPS signals. As mentioned above, locating a communications device is possible also using measurements relating to signals of a communications system. Rough location estimates for a communications device can alternatively be obtained based on the identities of the cell(s), via which a communications device is currently communicating. Until now the development of cellular network based LoCation Services (LCS) algorithms has been mostly focused towards algorithms capable of performing location calculations in a two-dimensional scenario. In other words, these algorithms assume that the Earth's surface locally flat, and they do not take into account the altitude fluctuations. Algorithm developers have devoted little attention to location calculation algorithms capable of estimating the location of a communications device in a tri-dimensional scenario because of a lack of a clear need for such algorithms. Furthermore, estimating a location of a communications device in tri-dimensions gives rise to technical challenges such as the increased complexity of full tri-dimensional location calculation algorithms and the need of additional measurements for estimating the third coordinate. Recently, however, the results of cellular network based LCS algorithms have been considered to be a valuable component of the location assistance data to be provided to a GPS receiver for MS-based or MS-assisted A-GPS location method. However, since the results of cellular network based LCS algorithms shall be represented in three-dimensions, a need has arisen for a feasible network based method for estimating the location of a communications device in three-dimensions. In accordance with a first aspect of the invention, there is provided a method for estimating altitude of a communications device, comprising the step of estimating the altitude of the communications device based at least on altitude of at least one antenna of the communications system, said communications device communicating with the communications system via said at least one antenna. In accordance with a second aspect of the invention, there is provided a method for providing location assistance information to a communications device communicating with a communications system via at least one antenna of said communications system, comprising estimating an altitude estimate for the communications device, and determining location assistance information based on a two-dimensional location estimate and the altitude estimate for the communications device. In accordance with a third aspect of the invention, there is provided a communications system, said communications system comprising storage means for storing antenna information representing at least altitudes of antennas of said communications system, and first estimation means for estimating an altitude of a communications device communicating with the communications system via at least one antenna of said communications system, said altitude estimation being based at least on altitude of said at least one antenna of said communications system. In accordance with a fourth aspect of the invention, there is provided a network element for a communications system, said network element comprising first determination means for determining antenna information representing at least altitudes of antennas of said communications system, and first estimation means for estimating the altitude of a communications device communicating with the communications system via at least one antenna of the communications system, said altitude estimation being based at least on altitude of said at least one antenna of said communications system. The altitude estimation may be based at least on altitudes of at least two antennas of the communications system, said communications device communicating with the communications system via said at least two antennas. The altitude estimation may be an average of altitudes of said at least two antennas. When there is provided a two-dimensional location estimate of the communications device and antenna information representing three-dimensional locations of said at least two antennas, the altitude estimation may be based on said two-dimensional location estimate of the communications device and on said antenna information. The altitude estimation may use a weighted average of altitudes of said at least two antennas, each weight taking into account said two-dimensional location estimate of the communications device and a two-dimensional location of an antenna of said communications device. Each weight in the weighted average may be inversely proportional to a distance between the two-dimensional location estimate of the communications device and the two-dimensional location of an antenna of said communications system. Alternatively, the altitude estimation may be determined by projecting the two-dimensional location estimate of the communications device to a reference plane determined using said antenna information. A method for estimating altitude of the communications device may further comprise the step of estimating said two-dimensional location estimate for the communications device. Accuracy of the altitude estimate of the communications device may be also estimated. Altitude of said at least one antenna may represents said at least one antenna at the ground level or above the ground level. Embodiments of the present invention provide an estimate for the three-dimensional location of a communications device by estimating the altitude of the communications device information about the altitude of at least one antenna of a communications system. A two-dimensional location estimate and information about the two-dimensional locations of antennas of a communications system may optionally be used. An estimate for three-dimensional location of a communications device can be obtained using the same measurements that have been made for estimating the two-dimensional location of the communications device. There is thus no need for modifying cellular network configuration or design for estimating the location of the communications device in three dimensions. Embodiments of the invention also overcome some technical challenges relating to estimating a location of a communications device in three dimensions. Especially the amount of measurements needed for locating a communications device in three dimensions is not increased from the amount of measurements needed for the two-dimensional location estimate. In fact, once a two-dimensional location estimate is provided there is no need to perform measurements. Furthermore, as height and altitude distribution of antennas of a communication system is typically very small compared to the distribution of the antennas in the horizontal direction, the accuracy of full tri-dimensional location calculation algorithms is quite poor even though the full tri-dimensional location calculation algorithms are quite complex. Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: In the description below, reference is made to a GSM network and to a UMTS network. These networks are to be understood as examples of a communications network, where the present invention is applicable. It is appreciated that the names of the network elements of a cellular telecommunications network may vary. The naming of the network elements in connection with Location services architecture is logically implemented in the cellular telecommunications network For positioning a communications device using a satellite positioning system and with the location assistance information provided from a communications system, the communications devices needs to be provided with functionality to receive and process signals from satellite positioning system satellites and with functionality to receive and process signals from the communication system. For facilitating detailed discussion on estimating the location of the communications device in three dimensions, reference is made to The geoid is the particular equipotential surface of the Earth's gravity field that is closely associated to the mean ocean surface. The geoid has been traditionally used as a reference surface for the mean sea level and it is expressed at a given point in terms of the geoid undulation N, which is the distance above (+N) or below (−N) the reference ellipsoid (see The height of a point on the Earth's surface (see, for example, P The expression above indicates that the geodetic height of a point on the Earth's surface is a good approximation of the height measured along the line of gravity through the point itself. The line of gravity trough point P Given a certain point P above or below the Earth's surface (see The upper part of The upper part of For estimating the altitude of a communications device UE, it is here assumed that a two-dimensional location estimate for the communications device is available and that the communications device is on the ground level. Given these assumptions, the problem discussed here consists in estimating the UE altitude rather than its height above the reference ellipsoid. It is appreciated that especially for the purpose of providing location assistance information for Assisted GPS, the altitude estimate for the communications device may be quite rough, so the assumption about the communications device being on the ground level is acceptable. In addition to the two-dimensional location estimate, a corresponding confidence region may have been calculated beforehand and may be available. The available two-dimensional UE location information is typically represented in an xy Cartesian reference system, which is a local plane approximation of the reference ellipsoid (see The tri-dimensional location estimate is obtained by modeling the ground level with a certain reference plane (RP). Some possible definitions for the reference plane are discussed, by the way of example, in more detail below. Since the reference plane is an approximation of the Earth's surface and since the UE is assumed to be located on the Earth's surface, the UE altitude is calculated by assuming that the available two-dimensional location estimate is a projection over the xy plane of the tri-dimensional location lying on the reference plane (see Once the reference plane is defined, the computation of the altitude estimate â In a first alternative, the reference plane is assumed to be a plane parallel to the yx plane. The z coordinate of the reference plane is equal to a weighted average of the antennas' altitudes:
A second alternative for the reference plane definition is suitable for a situation, where the antenna sites involved in the altitude estimation calculations are aligned. In other words, the antenna sites lie on a straight line. In this case is it possible to define the reference plane to be a plane, where this straight line connecting the antenna sites lies. As the line connecting the sites does not define a plane unambiguously, a further restriction needs to be posed. Two examples of such a restriction are that the xy plane is tilted along a line parallel either to x axis or y axis for making the line connecting the antenna sites to lie in the reference plane. A third alternative for the reference plane is applicable, when three non-aligned antenna sites are involved in estimating the altitude of the communications device. In this case, the reference plane may be defined by the analytical expression given by the following determinant:
A fourth alternative for the reference plane is applicable, when four or more non-aligned antenna sites are involved in estimating the altitude of the communications device. In this case, the reference plane may be defined as the regression plane
In addition to a two-dimensional location estimate for the communications device, an estimate for the uncertainty or accuracy of the two-dimensional location estimate may be available. The combination of the two-dimensional location estimate and of the confidence region is often referred to as a shape. Table 1 below lists some examples of shapes in the left-hand column. Typically a location estimation algorithm used in cellular telecommunication network can produce at least one of these shapes. Some of the shapes are discussed in more detail in 3GPP Technical specification TS 23.032 “Universal Geographical Area Description (GAD) (Release 4)” , V4.1.1, in Section 5. It is noted that any one of the shape types listed in the left-hand column of Table 1 may be supported by any method of estimating location of a communications system in two dimensions. It is noted that the geographical coordinates of the shapes may be expressed, for example, in a same local Cartesian reference system used to represent the coordinates of network elements, or, as a second example, in a geodetic format including latitude and longitude. If the estimation of the altitude of a communications device is performed in a local Cartesian reference system, the shape is preferably expressed in the same local Cartesian reference system or alternatively converted to this format. It is also noted that the orientation angles included in the shapes may be measured, for example, in radians counterclockwise from the x-axis of the Cartesian reference system, or as a second example, in degrees clockwise from North. The shape types in Table 1 are, by the way of example, expressed in a Cartesian coordinate system. The first shape type in Table 1 is a Cartesian Point, which corresponds to the “Ellipsoid Point” Shape defined in TS 23.032. The Cartesian Point type defines a point (x The second shape type in Table 1 is a Cartesian point with uncertainty Ellipse, which corresponds to the “Ellipsoid Point with uncertainty Ellipse” shape defined in TS 23.032. This “Cartesian point with uncertainty Ellipse” shape type has the following parameters: the Cartesian coordinates of an origin (generally the location estimate); a semi-major axis R The third shape type in Table 1 is a Cartesian polygon and the fourth shape type in Table 1 is a Cartesian point with uncertainty Polygon. The difference here is that the fourth shape has coordinates (x The fifth shape type in Table 1 is a Cartesian Arc, and it correspond to the “Ellipsoid Arc” defined in TS 23.032. The Cartesian arc is defined by the following coordinates: the Cartesian coordinates of an origin (x The sixth type is a Cartesian point with the uncertainty Arc. This shape type includes Cartesian coordinates of a location estimate, x In the following it is discussed how to determine an estimate of vertical uncertainty of the altitude estimate for the communications device. One option is to project the uncertainty area (confidence region) to the reference plane.
Further options for estimating uncertainty of the altitude estimate for the communications device are discussed next in connection with an uncertainty ellipsoid shown in the lower part of Define first a horizontal acceptance region enclosed within the two planes z=z For each of the N A first alternative for estimating the vertical uncertainty is simply to use the acceptance region AR. This is illustrated in the upper part of A second alternative for estimating the vertical uncertainty is simply to draw lines in the uz plane (see the upper part of A third alternative for estimating the vertical uncertainty is illustrated in When all steps above are completed for all cells, select the intersection with largest distance from the location estimate among the intersections selecting for each cell. The distance of the intersection selected from the reference plane defines the vertical uncertainty of the uncertainty ellipsoid. The resulting ellipsoid will include, if not all, large part of the rectangle defined by the extremes of the segments s In the example in The algorithm described above does not provide any indication on the value of parameter L, used to define the length of segments s Once the sphere is defined, the value of L can be calculated as the height of the projection on the sphere of the point (u=u It is appreciated that the vertical certainty relating to a two-dimensional uncertainty ellipse need not be estimate exactly in one of the ways discussed above, but other variations are also possible. The right-hand column of Table 1 indicates parameters added to the two-dimensional location estimate information for obtaining three-dimensional location estimates. In step The functionality relating to estimating the altitude of a communications device is typically provided in a location server, for example in a Mobile Location Center. The functionality of a location server may be incorporated to a further network element, for example to a network element responsible for radio resource control in a cellular telecommunications network. Block Block As mentioned above, the two-dimensional location estimate may be determined as part of the same process as the altitude estimation. The two-dimensional location estimate for the communications device may be determined based on signal timing measurements, signal strength measurements, and/or direction of arrival measurements relating to at least one antenna of the communications system. Alternatively, the two-dimensional location estimate may be based on the cell identity of at least one antenna via which the communications device is communicating. It is appreciated that although in the above description reference is made mainly to the GSM and UMTS cellular telecommunications systems, the present invention is applicable also in other communications systems. The term communications device in this description and in the appended claims refers to any device capable of communicating via a communications system. Examples of such communications devices are, for example, a mobile phone, a PDA (personal digital assistant) device, a portable computer, a mobile terminal or any other type of user equipment. It is appreciated that estimation of the altitude of a communications device may be performed in another coordinate system than in the local Cartesian coordinate system. It is noted, however, that the reference plane is straightforward to construct in the Cartesian coordinates. Other reference surfaces may be usable in other coordinate systems. It is also appreciated that information about antennas may represent antenna locations or antenna site locations on the ground level. If it is assumed that the communications device is on the ground level, the antenna site information is typically used in calculating the altitude estimate for the communications device. If information about the sum of the antenna altitude a and antenna height h, it may be possible to estimate the antenna site altitude on the ground level before estimating the altitude for the communications device. On the other hand, altitude estimation of a communications device may be based on true three-dimensional antenna locations above the ground level, not on antenna site locations on the ground level. For example, if it is known that all cells involved in the two-dimensional location estimate calculations or in the altitude estimation calculations relating to a communications device are indoor cells, the altitude estimation of the communications device may be based on the known true antenna locations, not on antenna locations on the ground level. Examples of indoor cells are, for example, cells in an office building or in a hospital. A communications system may store information relating to the type of the cells, and this information may comprise indication of a cell being an indoor cell or an outdoor cell. Such indication about indoor/outdoor cells may be used in the altitude estimation for a communications device. Although preferred embodiments of the apparatus and method embodying the present invention have been illustrated in the accompanying drawings and described in the foregoing detailed description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the spirit of the invention as set forth and defined by the following claims. Patent Citations
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